1. Field of the Invention
The present invention relates to welding practice, and particularly to a method of surfacing to build up a surface layer having different-composed portions and apparatus for carrying out the same.
When building up a surface layer having different-composed portions the weld pool volume influences the size of the transition zone between different-composed portions. This transition zone is always large, which prevents the formation of the surface layer having distinct boundary between the portions having different composition and, hence, different properties. In other words, lack of sharp transition between different portions does not allow producing a surface layer which would feature sufficiently high properties.
2. Prior Art
There is known a method of surfacing with alternating composition (cf. Teoretitcheskie i tekhnologitcheskie osnovy naplavki. Novye protzessy mekhanizirovanoi naplavki. Pod red. I. I. Furmana, Kiev, izd. IES im. E. O. Patona AN USSR, 1977, pp. 102-108), wherein the transition zone is made shorter by varying the amount of alloying elements fed to the weld pool with respect to the amount of these alloying elements required in certain portions of the surface layer being formed. The amount of the elements being fed to the weld pool is varied by a value which is proportional to the forward derivative of the desired law of variation of these elements in the surface layer being formed. In case the composition and, hence, properties to the surface layer being formed has to be varied to a great extent the above method does not yield the desired results, which is due to a limited content of the alloying elements contained in the real electrode and filler materials as well as a limit rate of feeding these materials to the weld pool. With the chemical composition of the surface layer being varied discretely the quantity of the alloying elements being fed to the weld pool according to the prior art approaches infinity, while the duration of their being fed approaches zero, which is not practicable.
There is also known a device for surfacing with alternating composition. ("Avtomaticheskaya svarka", 1978, No. 3, pp. 59-60) permitting the feed rate of electrodes and fillers to be varied in the course of surfacing. This device comprises an actuating mechanism for delivering electrode and filler materials, connected with a control device controlled by a surfacing rate regulating unit through a programmer connected with a comparator device.
However, the prior art apparatus has a limited capability of controlling the size of the transition zones, which capability is determined by the surfacing process that they are designed to carry out.